1. Field of the Invention
The present invention relates to a display panel and in particular, to a panel for an organic light emitting diode display.
2. Discussion of the Background
Generally, an organic light emitting diode (OLED) display is a self emissive display device that displays images by exciting an emissive organic material to emit light. A light emitting element of an OLED display includes an anode (hole injection electrode), a cathode (electron injection electrode), and an organic light emission layer interposed therebetween. When holes and electrons are injected into the light emission layer, they recombine and emit light when transitioning from an excited state to a ground state. The organic light emission layer may further include one or more of an electron transport layer (ETL) and a hole transport layer (HTL) as well as an electron injecting layer (EIL) and a hole injecting layer (HIL) for enhancing the light emission.
The OLED display includes a plurality of pixels, and each pixel includes an anode, a cathode, and a light emission layer. The pixels may be arranged in a matrix, and they may be driven in passive matrix (or simple matrix) addressing or active matrix addressing.
The passive matrix OLED display includes a plurality of anode lines, a plurality of cathode lines intersecting the anode lines, and a plurality of pixels, each including a light emission layer. Selecting an anode line and a cathode line causes a pixel located at the intersection of the selected signal lines to emit light.
The active matrix (AM) OLED display includes a plurality of pixels, and each pixel may include a switching transistor, a driving transistor, and a storage capacitor as well as an anode, a cathode, and a light emission layer. The AM OLED display further includes a plurality of gate lines transmitting gate signals and a plurality of data lines transmitting data voltages. The switching transistor is coupled to a gate line and a data line, and it transmits the data voltage from the data line in response to the gate signal from the gate line. The driving transistor receives the data voltage from the switching transistor and drives a current having a magnitude corresponding to the data voltage. The current from the driving transistor enters the light emission layer to cause light emission having an intensity depending on the current. The storage capacitor is coupled between the data voltage and a supply voltage to maintain their voltage difference. The gray scaling of the AM OLED display is accomplished by controlling the data voltages to adjust the current driven by the driving transistor. The OLED display represents colors by providing red, green and blue light emission layers.
Additionally, OLED displays may be top emission and bottom emission displays depending on a light emitting direction. The top emission OLED display includes a transparent cathode, which is usually made of indium tin oxide (ITO) or indium zinc oxide (IZO), and an opaque anode. Conversely, the bottom emission OLED display includes an opaque cathode and a transparent anode. The relative positions of the anode and the cathode may be altered if required.
The cathode is supplied with a common voltage through another conductor, and the contact resistance between the cathode and the conductor may be high.